Current anaerobic digester technology can convert organic waste into the energy carrier methane. However, methane is not an ideal transportation fuel and the economic value of methane is too low to support widespread adaptation. In the last decade, especially in dry-mill technology (i.e., grinding kernel and subsequent yeast fermentation), funds for liquid biofuel production have been mostly invested in the corn kernel-to-ethanol industry. However, the net energy balance ratio (i.e., renewable energy out over nonrenewable energy in) has been low; in large part, because of the vast energetic costs to separate (i.e., distill) miscible ethanol.
Current practice and belief is that methanogenesis should be completely inhibited during production of medium chain carboxylates. Medium-chain carboxylic acids, such as n-caproic acid, are commodity chemicals that are already used in lubricants, personal care products, animal feed additives, and antimicrobials. The C6 carboxylate, n-caproic acid, can be converted to a fuel by, for example, a series of ketonization and dehydrogenation processes to generate alkanes (C11 alkane is a drop in fuel). These alkanes can be blended with other chemicals to produce a transportation fuel, such as biodiesel. The value of n-caproic acid is already 20 times higher than methane. The relatively low maximum solubility of n-caproic acid makes extraction easier and with a much lower energy footprint compared to distillation of miscible ethanol.
Although the value of medium chain carboxylates as energy chemicals is recognized, efficient and economically feasible methods for producing these are not available. Fermentation of lignocellulosic substrates to carboxylic acid acids (e.g., acetate, butyrate) has not been very efficient. Additionally, carbon is lost as CO2. The same is true for anaerobic digestion: digestion of carbohydrates results in methane while half of the input carbon is lost as CO2.